Paeoniflorin and liquiritin, two major constituents in Chinese herbal formulas used to treat hyperprolactinemia-associated disorders, inhibits prolactin secretion in prolactinoma cells by different mechanisms.

ETHNOPHARMACOLOGICAL RELEVANCE: Paeoniflorin and liquiritin are major constituents in some Chinese herbal formulas, such as Yiru Tiaojing (YRTJ) Granule (a hospitalized preparation) and Peony-Glycyrrhiza Decoction, used for hyperprolactinemia-associated disorders. AIM OF THE STUDY: To investigate the effect of paeoniflorin and liquiritin on prolactin secretion. MATERIALS AND METHODS: The effect of YRTJ Granule on metoclopramide-induced hyperprolactinemia was tested in rats. Paeoniflorin and liquiritin in the YRTJ Granule extract were identified and quantified by HPLC. The effects of paeoniflorin and liquiritin on prolactin secretion were examined in prolactinoma cells that were identified morphologically and by Western blot. The concentration of prolactin was determined by ELISA. The gene expression was analyzed by Western blot. RESULTS: YRTJ Granule ameliorated metoclopramide-induced hyperprolactinemia in rats. The contents of paeoniflorin and liquiritin in YRTJ Granule were 7.43 and 2.05mg/g extract, respectively. Paeoniflorin, liquiritin and bromocriptine (a dopamine D2 receptor (D2R) agonist) decreased prolactin concentration in MMQ cells expressing D2R. However, the effect of liquiritin and bromocriptine was abolished in GH3 cells lacking D2R expression. Interestingly, paeoniflorin still decreased prolactin concentration in GH3 cells in the same manner. Furthermore, paeoniflorin suppressed prolactin protein expression, and was without effect on D2R protein expression in both MMQ and GH3 cells. CONCLUSIONS: The present results suggest that paeoniflorin and liquiritin play a role in YRTJ Granule-elicited improvement of hyperprolactinemia. While the effect of liquiritin is D2R-dependent, paeoniflorin D2R-independently inhibits prolactin secretion in prolactinoma cells that may especially benefit the hyperprolactinemic patients who are refractory to dopaminergic therapies.

Efficacy and Mechanism of Action of Yiru Tiaojing Granule Against Hyperprolactinemia In Vitro and In Vivo.

Yiru Tiaojing Granule, a traditional Chinese medicine formula, is used to treat hyperprolactinemia. This study was conducted to evaluate the mechanism of action and pharmacological activity of Yiru Tiaojing Granule on prolactin secretion. The animal model of hyperprolactinemia was induced by metoclopramide. The dopamine D2 receptor in hyperprolactinemia rat models was analyzed by immunohistochemistry. The biochemical parameters, including a follicle-stimulating hormone, luteinizing hormone, estradiol, progesterone, testosterone, and prolactin, were measured by an enzyme-linked immunosorbent assay. Furthermore, the expression of prolactin and the dopamine D2 receptor was analyzed by Western blotting. The components in the Yiru Tiaojing Granule-medicated serum were assayed by liquid chromatography-tandem mass spectrometry. The Yiru Tiaojing Granule significantly decreased the prolactin level in the hyperprolactinemia rat model, and increased the estradiol, luteinizing hormone, and progesterone levels. The high and medium doses of Yiru Tiaojing Granule reduced dopamine D2 receptor expression in the brain (p < 0.001) and produced a similar effect on bromocriptine (p < 0.001). Yiru Tiaojing Granule-medicated serum reduced (p < 0.001) prolactin expression in MMQ cells in a concentration-dependent manner, but had no effects on GH3 cells. The level of the dopamine D2 receptor in MMQ cells was also increased dose-dependently (p < 0.05). In addition, the protein kinase A and cyclic adenosine monophosphate in MMQ cells were significantly attenuated dose-dependently by treatment with a high and medium dose of Yiru Tiaojing Granule-medicated serum (p < 0.05) and bromocriptine-medicated serum (p < 0.01). The results suggested that Yiru Tiaojing Granule was effective against hyperprolactinemia, and the activation of the dopamine D2 receptor, which was related to the second messenger cyclic adenosine monophosphate and protein kinase A, might be the potential mechanism.